Electrode comprising a head and a detachable plug

ABSTRACT

A connection between an electrode head and a cable plug to form an electrode plug head. The connection is a good electrical connection of a first contact and a second contact coaxially arranged about the first contact of the electrode head respectively with an inner terminal and an outer terminal of the cable plug similarly arranged. Further, a plastic casing enveloping the whole unit of electrode head clampingly engages another plastic casing enveloping the entire cable plug. The casings cause simultaneous engagement of an outer thread and an o-ring of the electrode head respectively with an inner thread and a shoulder of the cable plug. Thus, a fluid-proof electrode plug head is obtained. The electrode head is also provided with a thin metallic shield which is slidably mounted on the inner wall of the plastic casing and which is electrically connected to the second contact to serve as an electric shield so that the electrode plug head will be leak-proof when the electrode head and the cable plug are connected.

Detemple et al.

[ ELECTRODE COMPRISING A HEAD AND A DETACHABLE PLUG [76] Inventors:Manfred F. Detemple, 65 Mainz,

Josefstr. 65, Mainz; Horst Hubner, 6203 Hochheim, Herderstr. 8,Hochheim; Johann Oswald, 65 Mainz, Sommerringplatz 6, Mainz, all ofGermany [22] Filed: Oct. 12, 1972 [21] Appl. No.: 296,968

[30] Foreign Application Priority Data Mar. 3, 1972 Germany 7208139 [52]U.S. Cl 339/143 R [51] Int. Cl l-l0lr 13/46 [58] Field of Search 339/143R, 177, 60, 94

[56] References Cited UNITED STATES PATENTS 2,1 l9,452 5/l938 Woodhead339/60 R 2,742,622 4/l956 Stevens, Jr. 33 /94 R 3,l24,406 3/1964 Cook339/l43 R 3,643,208 2/1972 Massa, Jr. 33 /143 R "ll l lli Aug. 27, 1974Primary Examiner-James R. Boler Assistant Examiner-Peter NerbunAttorney, Agent, or Firm'Littlepage, Quaintance, Murphy & DobynsABSTRACT A connection between an electrode head and a cable plug to forman electrode plug head. The connection is a good electrical connectionof a first contact and a second contact coaxially arranged about thefirst contact of the electrode head respectively with an inner terminaland an outer terminal of the cable plug similarly arranged. Further, aplastic casing enveloping the whole unit of electrode head clampinglyengages another plastic casing enveloping the entire cable plug. Thecasings cause simultaneous engagement of an outer thread and an o-ringof the electrode head respectively with an inner thread and a shoulderof the cable plug. Thus, a fluid-proof electrode plug head is obtained.The electrode head is also provided with a thin metallic shield which isslidably mounted on the inner wall of the plastic casing and which iselectrically connected to the second contact to serve as an electricshield so that the electrode plug head will be leak-proof when theelectrode head and the cable plug are connected.

PATENTEU M19 2 7 7 FIG. 2

FIG.1

ELECTRODE COWRISING A IEAD AND A DETACI-IABLE PLUG DISCLOSURE Thepresent invention relates to a novel electrode such as a combinedmeasuring electrode and single-rod measuring chains. In such measuringelectrodes, it is customary to provide in one part, i.e., in theso-called electrode head, by soldering or welding together, a fixedelectric connection between the contact wires located in the electrode,and the so-called contact or connection cable. Occasionally theelectrical connection is provided by pressure contacts or by soldered-onor welded-on contacts at the contact cable and at the contact wireslocated in the electrode. In all cases, however, the contact cable isfixed in the electrode head in such a manner that cable and electrodetogether form a unit.

Since measuring electrodes normally have a high internal resistance 2lOMQ), it is customary to employ, for the purpose of electrostaticshielding, a shielded cable, a so-called coaxial cable, as constantcable. The cable core is connected to the measuring system proper, andthe electrostatic shield surrounding the cable core and usuallyconstructed as a dense copper lattice, is electrically connected eitherto the electrostatic shield, which in the electrode surrounds themeasuring system concentrically, or in the case of singlerod measuringchains, to the reference system which functions also as a shield.

In similarly constructed measuring systems, such as conductivity cells,double platinum electrodes for polarization current or polarizationvoltage titrations, and thermometer probes, the connection is frequentlyproduced in the manner described above.

A further possibility of providing a connection consists in the use ofelectrode heads shaped as plug sockets or screw clamps. In this case,coaxial connections may also be involved, the contact for the measuringelectrode being arranged, corresponding to the structure of the coaxialcable, in the plug center. The contact surface for the shield, whichusually constitutes also the outer casing of the plug head, issurrounded by an insulating material and is arranged concentricallyabout the middle contact.

Electrodes having a rigidly connected cable present the followingdisadvantages: Cable replacement is not possible complicating contactplug replacement. When the electrode becomes defective, the cable andusually also the connecting plug are thrown away. Due to the permanentfixation of the cable, the electrode cannot easily be stored in a stateready for measurement. This is especially troublesome when the cable islong.

Prior art electrode connections present at least one of the followingdisadvantages:

First, the shield, i.e., in single-rod measuring chains the referenceelectrode contact, is not an insulated outer casing. When a moisturelayer from the measuring solution or from a reinforcement in conductiveconnection to the electrode head is present, the reference system isshort-circuited by way of the resulting shunt resistance.

Second, the known plug connections are not sufficiently moisture vaportight to maintain the insulation resistance between cable core andshield necessary for the measurement and amounting to B 5 X 10 ohmcannot be maintained in the plug head.

To be sure, the electrode heads are insulated toward the outside but theshield located in the head is not sufficient, so that in the case ofstrong field changes, e.g., when the head is touched, the accuracy ofthe measuring result is adversely influenced. The known construction isso complicated and so difficult to manufacture and to connect that theexpenditure affects the price of the electrode disadvantageously.

It is an object of the present invention to provide an improvedelectrode substantially free of one or more of the disadvantages ofprior electrode connections. These disadvantages are overcome accordingto the present invention in that:

1. The connection between the electrode head and the electrode cable isa plug and screw connection;

2. The plug and head are both embedded in plastic. The screw thread alsoconsists of plastic;

3. An additional shield is provided in the electrode head in the form ofa metal casing which is arranged coaxially about the two contacts of theelectrode head and is electrically connected to the coaxial portion ofthe coaxial socket; and

4. The connection of the electrode head to the inner conductors thereofis a plug connection.

The plug and screw connection of the present invention is a coaxial one:One of the contacts of the cable plug inserted in a plastic cap, whichcontact in the cable constitutes a central wire, ends in the plug in anarrow metal casing surrounded by an insulating cover. The secondcontact of the cable plug forms a wider metal casing which is slid uponthis insulating cover.

Correspondingly, one of the contacts in the electrode head consists of acentral wire, which at its end is preferably fanned out, so that itclampingly engages the narrow casing of the cable plug, and the secondcontact consists of a metal casing which is so wide and provided withslots in such a way that the wider casing of the cable plug engageslikewise clampingly this casing of the electrode head.

The screw threads provided on the plug and head are of such dimensionsthat in the manufacture of the connection the contacts described above,of the two parts must first he slid into each other over a certainlength, e.g. about 2 mm, before the screw threads engage each other.Then the two parts are screwed together. For sealing purposes an O-ringof rubber or other plastic material is slid upon the outer thread. ThisO-ring has an outer diameter substantially equal to the outer diameterof the plastic casings of the head and the plug.

The arrangement described above of the contacts and threads, in whichthe central contact of the plug, shaped as a narrow casing, is slid uponthe wire-shaped middle contact of the electrode head, and thecasingshaped outer contact of the cable plug is inserted into a widercasing of the electrode head, and in which arrangement further an innerthread cut into the plastic casing of the cable plug is screwed upon anouter thread cut into the electrode head, may be entirely or partiallyreversed.

A particular characteristic of the present invention is that theelectrode head is provided with an electric shield which, in the shapeof a thin metallic casing, is mounted coaxially about the twoaforementioned terminals of the electrode head. This metal casing abutson the inside directly to the plastic wall of the electrode head, and inthe manufacture of the electrode head the plastic material is suitablyinjected directly into the metal casing.

A further characteristic of the present invention is that the connectionbetween the contacts of the electrode head and the contact wires issuingfrom the electrodes proper is a plug connection, that is to say, thecontacts of the electrode head end toward the inside in thin slottedmetal casings into which the wires issuing from the electrodes areclamped.

The shield casing described above is preferably shaped in such a waythat it envelops also this plug connection inside the electrode.

By means of the present invention various advantages are achieved: Thecombination of a plug connection and screw connection assures a goodelectrical contact between electrode head and cable plug and a safedamp-proof packing, to which result especially the O- ring contributes,and the long creepage path from the O-ring support by way of the plasticthread to the outer contact assures a safe protection. A liquid-proofclosure is of decisive importance for many fields of application ofmeasuring electrodes. For transportation or storing purposes, the plughead may likewise be closed, in a moisture-proof manner, with a closurecap capable of being screwed on. The packing is so good that, when asufficiently temperature-proof O-ring, eg from silicon plastic offluorelastomer is used, the packing assures, even in steamsterilization, the required high dielectric resistance in the electrodehead. The novel electric shield in the electric head prevents, asalready mentioned, outer electrical fields, which may occur when theelectrode head is being touched, from changing the measuring potential.The novel plug connection inside the electrode head makes possible aneasy assembly of the entire measuring electrode and simplifies electrodemanufacture.

The invention may be better understood by reference to the drawingswhere FIG. 1 is a partially cut away view of a head and FIG. 2 is apartially cut away view of a plug. Referring now to FIG. 1 it can beseen that the head comprises an inner contact 11 in the form of afanned-out wire which extends toward the inside into a thin casing 12.The latter holds the conductor 20 which is electrically connected to theelectrode (not shown). The head it further comprises a contact 13, ametal casing which changes likewise inside the electrode into a thincasing 14 capable of holding the second conductor of the head 10.Between the two contacts 11 and 13, a highly resistive insulator 19 isprovided. A metal casing 15 is mounted coaxially about the two contactsll and 13, which metal casing 15 serves as a shield and is connected inan electrically conductive manner to the outer contact 13. The wholeunit is enveloped by a plastic casing 16 having an outer thread 17. AnO-ring i8 is slid upon the shoulder between the outer thread 17 and theouter wall of the plastic casing 16.

Referring now to FIG. 2 there is shown a plug 30 comprising an innercontact 21, a narrow metal casing 22 to which the central wire (notshown) of the electrode cable is connected. The outer terminal consistsagain of a wider metal casing 23 which is electrically connected to theouter conductor of the cable. The whole unit is enveloped by a plasticcasing 26 into which the inner thread 27 is cut. Between the twocontacts 21 and 23 a highly resistive insulator 29 is inserted. Theplastic casing 28 is pressed by the metal part in a packing manneragainst the upper opening of the plastic casing.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that'variations and modifications can be effected within thespirit and scope of the invention as described above and as defined inthe appended claims.

What is claimed is:

1. An electrode comprising:

A. an electrode head comprising:

1. a first contact forming the core of the electrode head comprising afanned-out wire which ex tends toward the inside of the electrode headinto a thin casing;

2. a second contact which is a metallic casing arranged coaxially aboutthe first contact and provided with a slot formed by a thin bent wireextending inside the electrode head into a thin cas- 3. an insulatingplastic casing enveloping the whole unit of electrode head comprising anouter thread and a shoulder on an outer wall, and an O-ring upon theshoulder;

4. a highly resistive insulator disposed between the two said contacts;

5. a thin metallic casing electrically connected to the second contactand mounted coaxially about the two said contacts and abutting an insidewall of the plastic casing; and

B. a cable plug comprising:

6. an inner terminal, centrally disposed inside the electrode plug, inthe form of a narrow metallic casing that fits into the fanned-out endof the first contact of the electrode head;

7. an outer terminal, arranged coaxially about the inner terminal,having a wider metallic casing extending inside the cable plug;

8. an insulating plastic casing enveloping the entire cable plugcomprising an inner thread and a shoulder;

9. a highly resistive insulator disposed between the two said terminals,

wherein means for establishing an electrical connection between saidelectrode head and cable plug comprising clampingly engaging the twosaid plastic casings after the following connections take place:

a. the narrow metallic casing of the inner terminal of said cable plugclampingly engaged by the fanned-out end of the first contact of saidelectrode head,

b. the wider metallic casing of the outer terminal of said cable plugclampingly engaged by the slot provided in the second contact of theelectrode head,

c. the inner thread of the insulating plastic casing of the cable plugscrews into the outer thread of the insulating plastic casing of theelectrode head so that the O-ring of the electrode head rests againstthe shoulder of said plastic casing of the cable plug.

1. An electrode comprising: A. an electrode head comprising:
 1. a firstcontact forming the core of the electrode head comprising a fanned-outwire which extends toward the inside of the electrode head into a thincasing;
 2. a second contact which is a metallic casing arrangedcoaxially about the first contact and provided with a slot formed by athin bent wire extending inside the electrode head into a thin casing;3. an insulating plastic casing enveloping the whole unit of electrodehead comprising an outer thread and a shoulder on an outer wall, and anO-ring upon the shoulder;
 4. a highly resistive insulator disposedbetween the two said contacts;
 5. a thin metallic casing electricallyconnected to the second contact and mounted coaxially about the two saidcontacts and abutting an inside wall of the plastic casing; and B. acable plug comprising:
 6. an inner terminal, centrally disposed insidethe electrode plug, in the form of a narrow metallic casing that fitsinto the fanned-out end of the first contact of the electrode head; 7.an outer terminal, arranged coaxially about the inner terminal, having awider metallic casing extending inside the cable plug;
 8. an insulatingplastic casing enveloping the entire cable plug comprising an innerthread and a shoulder;
 9. a highly resistive insulator disposed betweenthe two said terminals, wherein means for establishing an electricalconnection between said electrode head and cable plug comprisingclampingly engaging the two said plastic casings after the followingconnections take place: a. the narrow metallic casing of the innerterminal of said cable plug clampingly engaged by the fanned-out end ofthe first contact of said electrode head, b. the wider metallic casingof the outer terminal of said cable plug clampingly engaged by the slotprovided in the second contact of the electrode head, c. the innerthread of the insulating plastic casing of the cable plug screws intothe outer thread of the insulating plastic casing of the electrode headso that the O-ring of the electrode head rests against the shoulder ofsaid plastic casing of the cable plug.
 2. a second contact which is ametallic casing arranged coaxially about the first contact and providedwith a slot formed by a thin bent wire extending inside the electrodehead into a thin casing;
 3. an insulating plastic casing enveloping thewhole unit of electrode head comprising an outer thread and a shoulderon an outer wall, and an O-ring upon the shoulder;
 4. a highly resistiveinsulator disposed between the two said contacts;
 5. a thin metalliccasing electrically connected to the second contact and mountedcoaxially about the two said contacts and abutting an inside wall of theplastic casing; and B. a cable plug comprising:
 6. an inner terminal,centrally disposed inside the electrode plug, in the form of a narrowmetallic casing that fits into the fanned-out end of the first contactof the electrode head;
 7. an outer terminal, arranged coaxially aboutthe inner terminal, having a wider metallic casing extending inside thecable plug;
 8. an insulating plastic casing enveloping the entire cableplug comprising an inner thread and a shoulder;
 9. a highly resistiveinsulator disposed between the two said terminals, wherein means forestablishing an electrical connection between said electrode head andcable plug comprising clampingly engaging the two said plastic casingsafter the following connections take place: a. the narrow metalliccasing of the inner terminal of said cable plug clampingly engaged bythe fanned-out end of the first contact of said electrode head, b. thewider metallic casing of the outer terminal of said cable plugclampingly engaged by the slot provided in the second contact of theelectrode head, c. the inner thread of the insulating plastic casing ofthe cable plug screws into the outer thread of the insulating plasticcasing of the electrode head so that the O-ring of the electrode headrests against the shoulder of said plastic casing of the cable plug.